He said the average growth rate of private school fees in the senior years had outstripped rises in medical and hospital services.
But Independent Schools Victoria chief executive Michelle Green said predictions were fraught because schools also had to respond to external factors,including government funding and broader economic pressures,when setting fees.
''Really we're just interested in what's going to happen next year and the year after that and that's what parents are interested in. What happens to fees in 2016 will depend entirely on government funding and what happens to the economy,''she said.
Professor Hirschberg said competition between schools and limited places were driving increases.
''Since they compete against each other they have an incentive to hire better teachers and offer more subjects,''he said.
Year 12 fees for''day boarders''at Geelong Grammar School have already surpassed $32,000.